Lubricating oil composition

ABSTRACT

The present invention provides a lubricating oil composition that maintains properties necessary to lubricating a transmission and other devices and has more excellent insulation properties and anti-wear properties and more improved anti-seizure properties than the prior art and comprises (A) a lubricating oil base oil; (B) at least one type of phosphorus compound selected from the group consisting of phosphorus compounds having at least one hydroxyl group and/or at least one thiol group; and (C) an ashless dispersant having a functional group containing as a dispersion group in an amount of less than 0.001 percent by mass on the basis of nitrogen on the total composition mass basis or no such an ashless dispersant at all, the composition having a 80° C. volume resistivity of 5×10 8  Ω·m or greater.

TECHNICAL FIELD

The present invention relates to lubricating oil compositions withexcellent insulation properties and lubricity.

BACKGROUND ART

A variety of electronic control devices have been used in the mechanismsof an automobile. Some of them may be used in lubricating oil and thusthe insulation properties thereof have become important. In particular,lubricating oils for the transmission, both the transmission andelectric motor, or the device in which a lubricating system is shared bythe transmission and electric motor, mounted in a fuel cell electricvehicle, an electric vehicle or a hybrid vehicle have been required tohave higher insulation properties because these devices operate using ahigh electric voltage. Furthermore, in recent years, the transmissionhas been required to be improved in power transmission efficiency anddown-sized as well as weight-reduced so as to improve fuel efficiencyand thus has been applied with a higher load. The lubricating oil has,therefore, been demanded to have insulation properties as well as moreimproved anti-wear properties and anti-seizure properties.

In addition to the above-described properties, the lubricating oil fortransmissions are required to have friction characteristics conformingwith the characteristics of a clutch, viscosity characteristics rangingfrom low temperatures to high temperatures so that an appropriatehydraulic pressure control can be achieved, i.e., viscosity retentionwhich is not affected on temperature as much as possible, and oxidationstability and detergent dispersibility to keep the device clean so thatthe control device thereof can operate appropriately. Furthermore, thesecharacteristics are generally needed to be retained during the workinglife of the device. For this purpose, a variety of additives are used ina transmission lubricating oil.

So far, as such transmission lubricating oils, some oils have beenproposed such as an automobile transmission oil composition comprising abase oil selected from mineral oils, synthetic oils and mixtures thereofand a phosphorus compound selected from hydrocarbon group-containingzinc dithiophosphate, triaryl phosphate, triaryl thiophosphate and amixture thereof in an amount of 0.1 to 15.0 percent by mass on the totalmass composition basis and having a 80° C. volume resistivity of 1×10⁷Ω·m or greater (Patent Literature 1) and a transmission oil compositioncomprising a base oil selected from mineral oils, poly-α-olefins andhydrogenated compounds thereof, alkylbenzenes, ester-based compounds andmixtures thereof and having a 80° C. kinematic viscosity of 1.5 to 4.0mm²/s, a phosphorus compound selected from hydrocarbon group-containingzinc dithiophosphate, triaryl thiophosphates and mixtures thereof in anamount of 0.1 to 4.0 percent by mass on the total composition massbasis, and an ashless dispersant and having a 80° C. volume resistivityof 1×10⁸ Ω·m or greater (Patent Literature 2).

CITATION LIST Patent Literature

-   Patent Literature 1: WO2002/097017-   Patent Literature 2: Japanese Patent Application Publication    2008-285682

SUMMARY OF INVENTION Technical Problem

As described above, a variety of additives are used in a transmissionoil but would alone or in combination degrade the insulation properties,anti-wear properties or anti-seizure properties. The present inventionaims at providing a lubricating oil composition maintaining propertiesnecessary for a transmission and having more excellent insulationproperties and anti-wear properties and more improved anti-seizureproperties than the prior art.

Solution to Problem

That is, the present invention relates to a lubricating oil compositioncomprising: (A) a lubricating oil base oil; (B) at least one type ofphosphorus compound selected from the group consisting of phosphoruscompounds having at least one hydroxyl group and/or at least one thiolgroup; and (C) an ashless dispersant having a functional groupcontaining as a dispersion group in an amount of less than 0.001 percentby mass on the basis of nitrogen on the total composition mass basis orno such an ashless dispersant at all, the composition having a 80° C.volume resistivity of 5×10⁸ Ω·m or greater.

The present invention also relates to the above-described lubricatingoil composition wherein (B) the phosphorus compound having a hydrocarbongroup having 16 or fewer carbon atoms.

The present invention also relates to the above-described lubricatingoil composition used for the transmission, both transmission andelectric motor, or the device in which a lubricating system is shared bythe transmission and electric motor, mounted in a fuel cell electricvehicle, an electric vehicle or a hybrid vehicle.

Advantageous Effects of the Invention

The lubricating oil composition of the present invention maintainsproperties necessary to lubricate a transmission and other devices andhas more excellent insulation properties and anti-wear properties thanthe prior art and can be improved in anti-seizure properties.

DESCRIPTION OF EMBODIMENT

The present invention will be described in more detail below.

The lubricating base oil referred to as Component (A) used in thepresent invention may be a mineral base oil and/or a synthetic base oilor alternatively a mixture of two or more types of mineral oils orsynthetic base oils, or a mixture of a mineral base oil and a syntheticbase oil. The mix ratio in these mixtures may be selected arbitrarily.

Examples of the mineral lubricating base oil which may be used in thepresent invention include paraffinic or naphthenic mineral base oilswhich can be produced by subjecting a lubricating oil fraction producedby atmospheric- or vacuum-distillation of a crude oil, to any one of orany suitable combination of refining processes selected from solventdeasphalting, solvent extraction, hydrocracking, solvent dewaxing,catalytic dewaxing, hydrorefining, sulfuric acid treatment, and claytreatment; n-paraffins; and iso-paraffins. These base oils may be usedalone or in combination at an arbitrary ratio.

Examples of preferred mineral lubricating base oils include thefollowing base oils:

(1) a distillate oil produced by atmospheric distillation of a paraffinbase crude oil and/or a mixed base crude oil;

(2) a whole vacuum gas oil (WVGO) produced by vacuum distillation of thetopped crude of a paraffin base crude oil and/or a mixed base crude oil;

(3) a wax produced by a lubricating oil dewaxing process and/or aFischer-Tropsch wax produced by a GTL process;

(4) an oil produced by mild-hydrocracking (MHC) one or more oilsselected from oils of (1) to (3) above;

(5) a mixed oil of two or more oils selected from (1) to (4) above;

(6) a deasphalted oil (DAO) produced by deasphalting an oil of (1), (2)(3), (4) or (5);

(7) an oil produced by mild-hydrocracking (MHC) an oil of (6); and

(8) a lubricating oil produced by subjecting a mixed oil of two or moreoils selected from (1) to (7) used as a feed stock and/or a lubricatingoil fraction recovered therefrom to a normal refining process andfurther recovering a lubricating oil fraction from the refined product.

No particular limitation is imposed on the normal refining process usedherein. Therefore, there may be used any refining process having beenconventionally used upon production of a lubricating base oil. Examplesof the normal refining process include (a) hydro-refining processes suchas hydrocracking and hydrofinishing, (b) solvent refining such asfurfural extraction, (c) dewaxing such as solvent dewaxing and catalyticdewaxing, (d) clay refining with acidic clay or active clay and (e)chemical (acid or alkali) refining such as sulfuric acid treatment andsodium hydroxide treatment. In the present invention, any one or more ofthese refining processes may be used in any combination and order.

The mineral lubricating base oil used in the present invention isparticularly preferably a base oil produced by further subjecting a baseoil selected from (1) to (8) described above to the followingtreatments.

That is, preferred are a hydrocracked mineral oil and/or wax-isomerizedisoparaffinic base oil produced by hydrocracking or wax-isomerizing abase oil selected from (1) to (8) described above as it is or alubricating fraction recovered therefrom and subjecting the resultingproduct as it is or a lubricating fraction recovered therefrom todewaxing such as solvent dewaxing or catalytic dewaxing, followed bysolvent refining or followed by solvent refining and then dewaxing suchas solvent dewaxing or catalytic dewaxing. The hydrocracked mineral oiland/or wax-isomerized isoparaffinic base oil are used in an amount ofpreferably 30 percent by mass or more, more preferably 50 percent bymass or more, and particularly preferably 70 percent by mass or more, onthe total base oil mass basis.

The lubricating base oil referred to as Component (A) used in thetransmission lubricating oil composition of the present invention is alubricating base oil adjusted so that the 100° C. kinematic viscosity isfrom 1.5 to 4.5 mm²/s.

Component (A) is preferably one or more types selected from thefollowing (A-a) to (A-c):

(A-a) a mineral base oil having a 100° C. kinematic viscosity of between1.5 and lower than 3.5 mm²/s, preferably 1.9 to 3.2 mm²/s;

(A-b) a mineral base oil having a 100° C. kinematic viscosity of between3.5 and lower than 7 mm²/s, preferably 3.6 to 4.5 mm²/s; and

(A-c) a synthetic base oil having a 100° C. kinematic viscosity ofbetween 1.5 and lower than 7 mm²/s, preferably 3.8 to 4.5 mm²/s.

Mineral base oils (A-a) to (A-b) have a % C_(A) of preferably 2 or less,more preferably 1 or less, more preferably 0.5 or less, particularlypreferably substantially 0. Lubricating oil (A-c) has a % C_(A) ofsubstantially 0. The use of lubricating base oil (A) having a % C_(A) of2 or less renders it possible to produce a lubricating oil compositionwith an excellent oxidation stability.

The % C_(A) used herein denotes the percentage of the aromatic carbonnumber in the total carbon number, determined in accordance with ASTM D3238-85.

No particular limitation is imposed on the viscosity index oflubricating base oils (A-a) to (A-c), which is, however, preferably 80or greater, more preferably 100 or greater, particularly preferably 120or greater and usually 200 or less, preferably 160 or less. The use of alubricating base oil having a viscosity index of greater than 80 rendersit possible to produce a composition exhibiting excellent viscositycharacteristics from low temperatures to high temperatures. The use of alubricating base oil having a too high viscosity index results in a toomuch normal paraffins in the resulting composition and also deterioratesthe low temperature fluidity thereof.

No particular limitation is imposed on the sulfur content of mineralbase oils (A-a) to (A-b) used in the present invention, which is,however, preferably 0.05 percent by mass or less, more preferably 0.02percent by mass or less, particularly preferably 0.005 percent by massor less. The sulfur content of lubricating base oil (A-c) issubstantially 0%. Reduction of the sulfur content of Component (A)renders it possible to produce a composition having a more excellentoxidation stability.

In the present invention, any one or more of the above-described baseoils (A-a) to (A-c) may be used. Above all, preferably (A-a) and (A-b)and/or (A-c) are used in combination. When Component (A-a) and/orComponent (A-b) and Component (A-c) are used in combination, the contentof Component (A-c) is preferably 1 to 50 percent by mass, morepreferably 3 to 20 percent by mass, more preferably 3 to 10 percent bymass on the total base oil mass basis. In particular, blending ofComponent (A-c) in an amount of on the order of 3 to 10 percent by massrenders it possible to produce a composition exhibiting excellenteffects in fatigue life, low temperature characteristics, and oxidationstability at a low cost.

Lubricating base oil (A) used in the present invention has a 100° C.kinematic viscosity of preferably 1.5 to 4.5 mm²/s, more preferably 2.8to 4.0 mm²/s, particularly preferably 3.6 to 3.9 mm²/s. The use of alubricating base oil with a 100° C. kinematic viscosity of 4.5 mm²/s orlower renders it possible to produce a lubricating oil compositionhaving a smaller frictional resistance at lubricating sites because ofits small fluid resistance and thus having excellent low temperatureviscosity (for example, the −40° C. Brookfield viscosity is 20,000 Pa·sor less). The use of a lubricating base oil with a 100° C. kinematicviscosity of 1.5 mm²/s or higher renders it possible to produce alubricating oil composition which is sufficient in oil film formationand thus more excellent in lubricity and less in evaporation loss of thebase oil under elevated temperature conditions.

The synthetic oil referred to as (A-c) may be a synthetic lubricatingoil such as poly-α-olefins (1-octene oligomer, 1-decene oligomer,ethylene-propylene cooligomer) and hydrogenated compounds thereof;isobutene oligomers and hydrogenated compounds thereof; isoparaffins;alkylbenzenes; alkylnaphthalenes; alkyldiphenyl ethanes; monoisopropylbiphenyl; dimethyl silicone; diesters (ditridecyl glutarate,di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate anddi-2-ethylhexyl sebacate); polyol esters (trimethylolpropane caprylate,trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate andpentaerythritol pelargonate); polyoxyalkylene glycols; dialkyldiphenylethers; polyphenyl ethers; or a mixture thereof. Among these oils,preferably used are poly-α-olefins and hydrogenated compounds thereof;isobutene oligomers and hydrogenated compounds thereof; isoparaffins;alkylbenzenes; alkylnaphthalenes; alkyldiphenylethane; monoisopropylbiphenyl; and dimethyl silicone because they have a 80° C. volumeresistivity of 1×10¹³ Ω·m or greater and thus can enhance the insulationproperties of the resulting lubricating oil composition. In general,ester-based compounds have a 80° C. volume resistivity of on the orderof 1×10⁹ to 1×10¹³ Ω·m and are preferably those from which the remainingmoisture and impurities have been sufficiently removed.

The term “80° C. volume resistivity” used herein is measured inaccordance with JIS C 2101 24. (volume resistivity test).

The synthetic oil used in the present invention is preferably selectedfrom poly-α-olefins and hydrogenated compounds thereof, alkylbenzenes,ester-based compounds and mixtures thereof. In this case, the resultingcomposition can maintain low temperature fluidity and low volatility inwell-balance under the conditions where it is used.

Typical examples of poly-α-olefins include oligomers or cooligomers ofα-olefins having 2 to 32, preferably 6 to 16 carbon atoms, such as1-octene oligomer, 1-decene oligomer, ethylene-propylene cooligomer, andhydrogenated compounds thereof.

These synthetic oils may be used alone. No particular limitation isimposed on the viscosity thereof. However, synthetic oils with differentviscosities may be used in combination so that the 100° C. kinematicviscosity is adjusted to preferably from 1.5 to 4.5 mm²/s. This isbecause the combination of a synthetic oil having a high viscosity withthat of a low viscosity results in a base oil having a higher viscosityindex.

The lubricating oil base oil referred to as Component (A) in the presentinvention is as described above but is preferably mixed with a solventrefined base oil having a kinematic viscosity of 20 mm²/s to 50 mm²/s ifthe resulting composition has a problem in fatigue life. Furthermore, itis preferably mixed with such a solvent refined oil in such an extentthat the mixture is adjusted to have a % C_(A) of 2 or less and a 100°C. kinematic viscosity of 1.5 to 4.5 mm²/s.

The lubricating oil composition of the present invention contains (B) atleast one type of phosphorus compound selected from phosphorus compoundshaving at least one hydroxyl group and/or at least one thiol group.

The phosphorus compound referred to as Component (B) in the presentinvention is at least one type of compound selected from phosphoruscompounds represented by formula (1), phosphorus compounds representedby formula (2), amine salts thereof, and derivatives thereof.

In formula (1), X¹, X² and X³ are each independently oxygen or sulfurand at least one of them is preferably oxygen, at least one of R¹, R²and R³ is hydrogen and the others are hydrocarbon groups having 1 to 30carbon atoms.

In formula (2), X⁴, X⁵, X⁶ and X⁷ are each independently oxygen orsulfur (one or two of X⁴, X⁵ and X⁶ may be a single bond or (poly)oxyalkylene group) and at least one of them is preferably oxygen, atleast one of R⁴, R⁵ and R⁶ is hydrogen and the others are hydrocarbongroups having 1 to 30 carbon atoms.

Examples of the hydrocarbon groups having 1 to 30 carbon atoms for R¹ toR⁶ include alkyl, cycloalkyl, alkenyl, alkyl-substituted cycloalkyl,aryl, alkyl-substituted aryl, and arylalkyl groups. The hydrocarbongroups are preferably alkyl groups having 1 to 30 carbon atoms and arylgroups having 6 to 24 carbon atoms, more preferably alkyl groups having3 to 18 carbon atoms, more preferably alkyl groups having 4 to 12 carbonatoms.

Examples of phosphorus compounds represented by formula (1) includephosphorous acid; monothiophosphorous acid; dithiophosphorous acid;phosphorous acid monoesters, monothiophosphorous acid monoesters,dithiophosphorous acid monoesters, and trithiophosphorous acidmonoesters, each having any one of the above-described hydrocarbongroups having 1 to 30 carbon atoms; and phosphorous acid diesters,monothiophosphorous acid diesters, dithiophosphorous acid diesters, andtrithiophosphorous acid diesters, each having any two of theabove-described hydrocarbon groups having 1 to 30 carbon atoms; and amixture thereof.

In order to further enhance the properties such as high temperaturedetergency and oxidation stability in the present invention, preferablytwo or more, particularly preferably all of X¹ to X³ in formula (1) areoxygen.

Examples of phosphorus compounds represented by formula (2) includephosphoric acid; monothiophosphoric acid; dithiophosphoric acid;trithiophosphoric acid; tetrathiophosphoric acid; phosphoric acidmonoesters, monothiophosphoric acid monoesters, dithiophosphoric acidmonoesters, trithiophosphoric acid monoesters, and tetrathiophosphoricacid monoesters, each having any one of the above-described hydrocarbongroups having 1 to 30 carbon atoms; phosphoric acid diesters,monothiophosphoric acid diesters, dithiophosphoric acid diesters,trithiophosphoric acid diesters, and tetrathiophosphoric acid diesters,each having any two of the above-described hydrocarbon groups having 1to 30 carbon atoms; phosphonic acid, phosphonic acid monoesters, andphosphonic acid diesters, each having any one or two of theabove-described hydrocarbon groups having 1 to 30 carbon atoms; thephosphoric acid compounds exemplified above but having a(poly)oxyalkylene group having 1 to 4 carbon atoms; derivatives of thephosphorus compounds exemplified above, such as β-dithiophosphorylatedpropionic acid and reaction products of dithiophosphates and olefincyclopentadiene or (methyl)methacrylates; and mixtures thereof.

In order to further enhance the properties such as high temperaturedetergency and oxidation stability in the present invention, preferablytwo or more, more preferably three or more, particularly preferably allof X⁴ to X⁷ in formula (2) are oxygen. One or two of X⁴, X⁵ and X⁶ maybe a single bond or a (poly)oxyalkylene group.

Examples of the salts of phosphorus compounds represented by formula (1)or (2) include salts produced by allowing a nitrogen compound such asammonia or an amine compound having in its molecules only a hydrocarbongroup having 1 to 30 carbon atoms or a hydroxyl group-containinghydrocarbon group having 1 to 30 carbon atoms to react with a phosphoruscompound and neutralize the whole or part of the remaining acidhydrogen.

Specific examples of the nitrogen-containing compound include ammonia,monoamines, diamines, and polyamines. Preferred examples includealiphatic amines having an alkyl or alkenyl group having 10 to 20 carbonatoms, which may be straight-chain or branched, such as decylamine,dodecylamine, dimethyldodecylamine, tridecylamine, heptadecylamine,octadecylamine, oleylamine, and stearyl amine.

The phosphorus compound referred to as Component (B) is preferably atleast one type of compound selected from the group consisting of aminesalts of phosphorus compounds of formula (1) wherein all of X′, X² andX³ are oxygen and amine salts of phosphorus compounds of formula (2)wherein all of X⁴, X⁵, X⁶ and X⁷ are oxygen (one or two of X⁴, X⁵ and X⁶may be a single bond or a (poly)oxyalkylene group) because they areexcellent in oxidation stability.

Alternatively, the phosphorus compound referred to as Component (B) ispreferably a phosphorus compound of formula (2) wherein all of X⁴, X⁵,X⁶ and X⁷ are oxygen (one or two of X⁴, X⁵ and X⁶ may be a single bondor a (poly) oxyalkylene group), at least one of R⁴, R⁵ and R⁶ ishydrogen and the others are each independently a hydrocarbon grouphaving 1 to 30 carbon atoms in terms of oxidation stability.

The hydrocarbon group of the phosphorus compound referred to asComponent (B) has preferably 16 or fewer carbon atoms. This is based onthe fact that fewer the carbon atoms, higher the volume resistivity isas set forth in Table 1 below.

TABLE 1 Structure of phosphorus compound Diphenylhydrogen Trialkylphosphite Dialkylhydrogen phosphite phosphite Dialkyl acid phosphateStructure of hydrocarbon group iC8 nC12 nC18 iC4 iC8 nC18 phenyl NC10nC18 Garnbon number of hydrocarbon group 8 12 18 4 8 18 8 10 18 Volumeresistivity 10¹⁰ Ω · m 358 315 27.9 1200 104 12.8 800 1.44 1.4 *Phosphoric compounds were each dissolved in a base oil with thefollowing physical properties to compare the volume resistivity. Theywere each added in an amount of 100 mass ppm by phosphorus. Kinematicviscosity (40° C.) 19.7 mm²/s, Kinematic viscosity (100° C.) 4.3 mm²/s,Viscosity index 125, % C_(P) 78.5, % C_(N) 21.5, % C_(A) 0

In Table 1, the volume resistivity designates the value measured at anoil temperature of 80° C. in accordance with JIS C 2101 24. (volumeresistivity test). In the above examples, each of the phosphoruscompound was added and dissolved in a mineral base oil so that it iscontained in an amount of 100 mass ppm on the basis of phosphorus.

No particular limitation is imposed on the content of Component (B) thatis the above-described phosphorus compound of the lubricating oilcomposition of the present invention, which is, however, 0.01 percent bymass or more, preferably 0.02 percent by mass or more, particularlypreferably 0.03 percent by mass or more and preferably 0.1 percent bymass or less, more preferably 0.08 percent by mass or less, particularlypreferably 0.05 percent by mass or less on the basis of phosphorus onthe composition mass basis. If the content of the phosphorus compound isless than 0.01 percent by mass on the basis of phosphorus, the resultingcomposition would be less effective in anti-wear properties. Whilst, ifthe content of the phosphorus compound is more than 0.01 percent by masson the basis of phosphorus, the resulting composition would be poor ininsulation properties, degraded in oxidation stability and enhanced inaggressivity against sealing materials.

The lubricating oil composition of the present invention ischaracterized in that it contains (C) an ashless dispersant having afunctional group containing nitrogen as a dispersion group in an amountof less than 0.001 percent by mass on the basis of nitrogen on thecomposition mass basis or does not contain such an ashless dispersant atall.

As described above, the lubricating oil composition of the presentinvention contains (B) at least one type of phosphorus compound selectedfrom phosphorus compounds having at least one hydroxyl group and/or atleast one thiol group. The inclusion of the phosphorus compound enhancessignificantly the anti-wear properties and anti-seizure properties ofthe composition. However, this type of phosphorus compound degradesdrastically the volume resistance of the composition compared with aphosphorus compound having no hydroxyl group and/or thiol group if anashless dispersant having a functional group containing nitrogen as adispersion group is contained. Therefore, the composition containsnecessarily (C) an ashless dispersant having a functional groupcontaining nitrogen as a dispersion group in an amount of less than0.001 percent by mass on the basis of nitrogen on the composition massbasis or does not contain such an ashless dispersant at all in order toimprove the anti-wear properties and anti-seizure properties of thecomposition.

Examples of the ashless dispersant having a functional group containingnitrogen as a dispersion group referred to as Component (C) includesuccinimide, benzylamine, and polyamines, each having a hydrocarbongroup having 40 to 400 carbon atoms.

However, among these compounds, those having been modified to have astructure wherein nitrogen cannot constitute a salt structure togetherwith Component (B) that is the phosphorus compound are excluded from theexamples. Fox example, compounds wherein the amino group is acylated ormodified with a boron compound or a sulfuric compound and incapable ofconstituting a salt structure with Component (B) that is the phosphoruscompound are excluded.

What is meant by “containing an ashless dispersant having a functionalgroup containing nitrogen as a dispersion group in an amount of lessthan 0.001 percent by mass on the basis of nitrogen on the compositionmass basis” is a structure or amount wherein even though an ashlessdispersant has an amino group remained so as to be able to constitute asalt structure with Component (B) that is the phosphorus compound, thecontent thereof is such a level that the volume resistance at 80° C. ofthe resulting composition is 5×10⁸ Ω·m or greater. Specifically, theashless dispersant is contained in such an amount that nitrogen iscontained in an amount of less than 0.001 percent by mass, morepreferably less than 0.0008 percent by mass on the composition massbasis.

No particular limitation is imposed on the use of compounds with astructure of thiadiazole or triazole that is an amine-based anti-oxidantor a corrosion inhibitor because it can be ignored if the contentthereof is 1 percent by mass or less.

The lubricating oil composition of the present invention has a 80° C.volume resistivity of preferably 5×10⁸ Ω·m or greater, more preferably6×10⁸ Ω·m or greater, particularly preferably 10×10⁸ Ω·m or greater. Thecomposition having a 80° C. volume resistivity of 5×10⁸ Ω·m or greatercan keep the insulation properties high not only when it is fresh butalso when it is degraded thereby avoiding an electric motor from havinga trouble such as shorting out for a long period of time.

If necessary, the lubricating oil composition of the present inventionmay be blended with various additives such as viscosity index improvers,extreme pressure additives, dispersants other than the above-describeddispersant compounds, metallic detergents, friction modifiers,anti-oxidants, corrosion inhibitors, rust inhibitors, demulsifiers,metal deactivators, pour point depressants, seal swelling agents,anti-foaming agents, and dyes, alone or in combination in order tofurther enhance the properties of the composition or impart thecomposition with properties required for a lubricating oil.

Examples of the viscosity index improvers include non-dispersant ordispersant type poly(meth)acrylate; non-dispersant or dispersant typeethylene-α-olefin copolymers and hydrogenated compounds thereof;polyisobutylene and hydrogenated compounds thereof; styrene-dienehydrogenated copolymers; styrene-maleic anhydride ester copolymers;polyalkylstyrenes; and copolymers of (meth)acrylate monomers representedby formula (1) and unsaturated monomers such asethylene/propylene/styrene/maleic anhydride.

The amount of the viscosity index improver in the lubricating oilcomposition of the present invention is such an amount that theresulting composition has a 100° C. kinematic viscosity of 5 to 10mm²/s, preferably 6 to 9 mm²/s and a viscosity index of 120 to 270,preferably 150 to 250, more preferably 170 to 220. More specifically,the amount is 15 percent by mass or less, preferably 10 percent by massor less, more preferably 8 percent by mass or less and 2 percent by massor more, preferably 4 percent by mass or more, more preferably 5 percentby mass or more on the composition mass basis. An amount of more than 15percent by mass causes a too high viscosity while an amount of less than2 percent by mass causes a too high viscosity and thus cannot secure asufficient composition viscosity.

Examples of the metallic detergent include those such as alkaline earthmetal sulfonates, alkaline earth metal phenates, and alkaline earthmetal salicylates.

Any one or more compounds selected from these metallic detergents may becontained in an amount of usually 0.01 to 10 percent by mass, preferably0.1 to 5 percent by mass on the total composition mass basis.

The friction modifier may be any compound that has been generally usedas a friction modifier for lubricating oils. Specific examples includeamine compounds, imide compounds, fatty acid esters, fatty acid amides,and fatty acid metal salts, each having per molecule at least one alkylor alkenyl group having 6 to 30 carbon atoms, particularly astraight-chain alkyl or alkenyl group having 6 to 30 carbon atoms.

Any one or more compounds selected from these friction modifiers may becontained in an amount of usually 0.01 to 5.0 percent by mass,preferably 0.03 to 3.0 percent by mass on the total composition massbasis.

The anti-oxidant may be any anti-oxidant that has been usually used inlubricating oils, such as phenol- or amine-based compounds.

Specific examples of the anti-oxidant include alkylphenols such as2-6-di-tert-butyl-4-methylphenol; bisphenols such asmethylene-4,4-bisphenol(2,6-di-tert-butyl-4-methylphenol);naphthylamines such as phenyl-α-naphthylamine; dialkyldiphenylamines;zinc dialkyldithiophosphoric acids such asdi-2-ethylhexyldithiophosphoric acid; and esters of(3,5-di-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid) or(3-methyl-5-tert-butyl-4-hydroxyphenyl)fatty acid (propionic acid) witha monohydric or polyhydric alcohol such as methanol, octanol,octadecanol, 1,6-hexanediol, neopentyl glycol, thiodiethylene glycol,triethylene glycol and pentaerythritol.

Any one or more of compounds selected from these compounds may becontained in any amount, which is, however, usually from 0.01 to 5percent by mass, preferably from 0.1 to 3 percent by mass on the totalcomposition mass basis.

Examples of the corrosion inhibitor include benzotriazole-,tolyltriazole-, thiadiazole-, and imidazole-types compounds.

Examples of the rust inhibitor include petroleum sulfonates,alkylbenzene sulfonates, dinonylnaphthalene sulfonates, alkenyl succinicacid esters, and polyhydric alcohol esters.

Examples of the demulsifier include polyalkylene glycol-based non-ionicsurfactants such as polyoxyethylenealkyl ethers,polyoxyethylenealkylphenyl ethers, and polyoxyethylenealkylnaphthylethers.

Examples of the metal deactivator include imidazolines, pyrimidinederivatives, alkylthiadiazoles, mercaptobenzothiazoles, benzotriazolesand derivatives thereof, 1,3,4-thiadiazolepolysulfide,1,3,4-thiadiazolyl-2,5-bisdialkyldithiocarbamate,2-(alkyldithio)benzoimidazole, and β-(o-carboxybenzylthio)propionitrile.

The pour point depressant may be any of the known pour point depressantsselected depending on the type of lubricating base oil but arepreferably poly(meth)acrylates having a weight average molecular weightof preferably 20,000 to 500,000, more preferably 50,000 to 300,000,particularly preferably 80,000 to 200,000.

The anti-foaming agent may be any compound that has been usually used asan anti-foaming agent for lubricating oils. Examples of such ananti-foaming agent include silicones such as dimethylsilicone andfluorosilicone. Any one or more of compounds selected from thesecompounds may be contained in any amount.

The seal swelling agent may be any compound that has been usually usedas a seal swelling agent for lubricating oils. Examples of such a sealswelling agents include ester-, sulfur- and aromatic-based seal swellingagents.

The dye may be any compound that has been usually used and may beblended in any amount. The amount is usually from 0.001 to 1.0 percentby mass on the total composition mass basis.

When these additives are blended with the lubricating oil composition ofthe present invention, the corrosion inhibitor, rust inhibitor, andanti-foaming agent are each contained in an amount of 0.005 to 5 percentby mass, the pour point depressant and metal deactivator are eachcontained in an amount of 0.005 to 2 percent by mass, the seal swellingagent is contained in an amount of 0.01 to 5 percent by mass, and theanti-foaming agent is contained in an amount of 0.0005 to 1 percent bymass, all on the total composition mass basis.

EXAMPLES

The present invention will be described more specifically with referenceto the following Examples and Comparative Examples but not limitedthereto.

Examples 1 to 6 and Comparative Examples 1 to 5

Lubricating oil compositions according to the present invention(Examples 1 to 6) and those for comparison (Comparative Examples 1 to 5)were prepared in accordance with the formulations set forth in Table 2.The performances of each composition were evaluated with the followingtests. The results are set forth in Table 2.

TABLE 2 Compar- Compar- Compar- Compar- Compar- Total Base ative ativeative ative ative Base Oil Mass Exam- Exam- Exam- Exam- Exam- Exam-Exam- Exam- Exam- Exam- Exam- Oil Basis ple 1 ple 2 ple 3 ple 4 ple 5ple 6 ple 1 ple 2 ple 3 ple 4 ple 5 A-1 Base Oil 1 ¹⁾ inmass 100 100 100100 100 100 100 100 100 % A-2 Base Oil 2 ²⁾ inmass 100 % A-3 Base Oil 3³⁾ inmass 100 % Addi- Total mass % tives Composition Mass Basis B-1 Oilsoluble mass % 0.5 0.1 0.1 0.1 0.1 0.1 phosphorus additive 1 ⁴⁾ B-2 Oilsoluble mass % 0.1 phosphorus additive 2 ⁵⁾ B-3 Oil soluble mass % 0.1phosphorus additive 3 ⁶⁾ B-4 Oil soluble 0.3 phosphorus additive 4 ⁷⁾C-1 Ashless mass % 4 4 dispersant 1 ⁸⁾ C-2 Ashless 4 dispersant 2 ⁹⁾ D-1Viscosity mass % 12 12 12 17 12 12 12 12 12 12 12 index improver ¹⁰⁾Additive mass % 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 package ¹¹⁾P content of masspm 500 100 100 100 100 100 0 100 0 100 100 thecomposition Evalution results Four - ball test ¹²⁾ WL mm²/s 1961 19611961 1961 1961 1961 1961 1961 1961 1961 1961 LNSL % 785 785 785 785 785785 490 785 490 785 785 Four - ball (wear mm²/s 0.5 0.5 0.5 0.5 0.5 0.50.7 0.5 0.8 0.5 0.5 scar diameter) ¹³⁾ Volume resistivity ¹⁴⁾ 10¹⁰ 0.060.15 0.12 0.06 0.13 0.05 0.16 0.005 0.031 0.001 0.01 Ω · m ¹⁾ kinematicviscosity (40° C.) 19.7 mm²/s, kinematic viscosity (100° C.) 4.3 mm²/s,viscosity index 125, % C_(P) 78.5, % C_(N) 21.5, % C_(A) 0 ²⁾ kinematicviscosity (40° C.) 22.7 mm²/s, kinematic viscosity (100° C.) 4.3 mm²/s,viscosity index 102, % C_(P) 66.4, % C_(N) 29.0, % C_(A)4.6 ³⁾di-2-ethylhexyl azelate kinematic viscosity (40° C.) 10.1 mm²/s,kinematic viscosity (100° C.) 3.0 mm²/s, viscosity index 144 ⁴⁾ aminesalt of acidic phosphoric acid ester (P content: 10%, phosphoric acidester: 2-ethylhexy, amine: mixed amine of C11to14) ⁵⁾ hydrogenphosphite. isoC4 P content: 16% ⁶⁾ acidic phosphoric acid ester,2-ethylhexyl P: 9.4% ⁷⁾ trioleylphosphite P: 3.7% ⁸⁾ boronatedsuccinimide, PIB M_(W) 2000, bis type, TEPA crosslinking ⁹⁾ succinimide,PIB M_(W) 1000, bis type, TEPA crosslinking ¹⁰⁾ non-dispersant type PMAM_(W) 25,000 ¹¹⁾ containing Ca metallic detergent (0.1 mass %), metaldeactivator (0.1 mass %), anti-oxidant (2.0 mass %), anti-foaming agent( 30 mass ppm) ¹²⁾ 1800 rpm ¹³⁾ 392N, 1800 rpm, 80° C., 30 min ¹⁴⁾ inaccordance with JIS C2101, measured at 80° C.

APPLICABILITY IN INDUSTRY

The lubricating oil composition of the present invention is acomposition improved in anti-wear properties and anti-seizure propertiesand can be used as a lubricating oil for an electric motor-equippedvehicle such as an electric vehicle or a hybrid vehicle, an electricmotor oil, an oil both for a transmission and an electric motor, and anoil for a device wherein a transmission and an electric motor arepackaged in one and a lubricating system is shared by the transmissionand an electric motor.

The present invention can provide the above-described transmission,electric motor and device including the lubricating oil composition ofthe present invention and a method for lubricating, insulating andcooling the above-described transmission, electric motor and deviceusing the lubricating oil composition of the present invention.

1. A lubricating oil composition comprising: (A) a lubricating oil baseoil; (B) at least one type of phosphorus compound selected from thegroup consisting of phosphorus compounds having at least one hydroxylgroup and/or at least one thiol group; and (C) an ashless dispersanthaving a functional group containing as a dispersion group in an amountof less than 0.001 percent by mass on the basis of nitrogen on the totalcomposition mass basis or no such an ashless dispersant at all, thecomposition having a 80° C. volume resistivity of 5×10⁸Ω□m or greater.2. The lubricating oil composition according to claim 1, wherein (B) thephosphorus compound having a hydrocarbon group having 16 or fewer carbonatoms.
 3. The lubricating oil composition according to claim 1, whereinthe composition is used for the transmission, both transmission andelectric motor, or the device in which a lubricating system is shared bythe transmission and electric motor, mounted in a fuel cell electricvehicle, an electric vehicle or a hybrid vehicle.
 4. The lubricating oilcomposition according to claim 2, wherein the composition is used forthe transmission, both transmission and electric motor, or the device inwhich a lubricating system is shared by the transmission and electricmotor, mounted in a fuel cell electric vehicle, an electric vehicle or ahybrid vehicle.